Prostaglandin F2alpha induced luteolysis, hypothermia, and abortions in beagle bitches.

Luteal phase plasma progesterone was radioimmunoassayed in samples collected before, during, and after a 72 hr treatment period during which Beagle bitches received repeated i.m. injections of prostaglandin F2alpha (n=17) or saline (n=3). PGF2alpha (20 ug/kg every 8 hr or 30 ug/kg every 12 hr) was administered to 7 pregnant and 8 nonpregnant bitches during the mid or late luteal phase of the cycle (Day 25-58) and to 2 nonpregnant bitches during the early luteal phase (Days 5 and 20). Progesterone was depressed from pretreatment levels (3-40 ng/ml) in each of the 15 bitches given PGF2alpha after Day 25 of the cycle. Mean progesterone (ng/ml plasma) at -24, 0, 12, 24, 36, 48, 60, 72 and 96 hr from the initial PGF2alpha injection were 16.6, 15.6, 9.3, 5.1, 2.1, 1.5, 1.4, 1.1 and 1.1 (+/- 0.9, n=15). Thereafter, progesterone was nondetectable in the 8 nonpregnant bitches and in 4 pregnant bitches that aborted. Abortions occurred when progesterone was depressed to 0.6-1.4 ng/ml, 56-80 hr after starting PGF2alpha treatment on Days 33-53 of the cycle. Three pregnant bitches did not abort when progesterone was depressed to a mean low value of 2.1 ng/ml during PGF2alpha treatments begun on Day 31-40 of pregnancy. Progesterone in these bitches recovered to 5-10 ng/ml and was maintained until the normal prepartum decline. Since PGF2alpha can induce complete luteolysis it may be of use as an abortifacient in the bitch. A transient fall in rectal temperature occurred in each of 12 luteal phase bitches injected with PGF2alpha (20 ug/kg, i.m.). The hypothermia was detectable within 15 min, maximal at 45-60 min, and averaged 1.39 degrees similarly treated. In six luteal phase bitches, plasma progesterone fell 20-45% within the 15 min required to observe a consistent decline in rectal temperature following PGF2alpha administratic effect and dependent on a fall in progesterone.